Alaska Fisheries Science Center Survey protocol for the Alaska sablefish longline survey By Michael F. Sigler and Chris R. Lunsford Introduction Sablefish (Anoplopoma fimbria) are a commercially important fish species in the northeast Pacific Ocean. Found along the upper continental slope, in Alaska they are caught primarily by longlines. Catches in the Alaskan EEZ have averaged 15,000 mt in recent years with an annual value of about $100 million. The fishery has been managed by an Individual Fisheries Quota system since 1995. Fishery-independent longline surveys have been conducted annually since 1978 to assess the relative abundance of this valuable resource. The survey abundance indices are combined with age, length, and fishery data to estimate absolute abundance and recommend catch quotas with age-structured models. Since 1978, the U. S. National Marine Fisheries Service (NMFS), Alaska Fisheries Science Center (AFSC) has conducted annual longline surveys with Japan (Japan-U.S. cooperative longline survey, 1978-94) and alone (1987-present, domestic longline survey). The survey has covered the upper continental slope (1978-present) and selected gullies (1987- present) of the Gulf of Alaska and the upper continental slope of the eastern Bering Sea (1982- 94, biennially since 1997) and Aleutian Islands region (1980-94, biennially since 1996). A unique aspect of this survey is that the charter vessel retains most of the catch after the scientific data are recorded. The survey lasts three months. The survey is conducted jointly by two components of the AFSC: the Auke Bay Laboratory and the Resource Assessment and Conservation Engineering Division. History of survey Sablefish have been exploited since the end of the 19th century by U.S. and Canadian fishermen. The North American fishery on sablefish developed as a secondary activity of the halibut fishery of the United States and Canada. Initial fishing grounds were off Washington and British Columbia and from there spread to Oregon, California, and Alaska during the 1920's. Since then, and up to 1957, the sablefish fishery was exclusively a U.S. and Canadian fishery, ranging from off northern California northward to Kodiak Island in the Gulf of Alaska. Japanese longliners began operations in the eastern Bering Sea in 1958. As the fishing grounds in the eastern Bering Sea were preempted by expanding Japanese trawl fisheries, the Japanese longline fleet expanded to the Aleutian Islands region and the Gulf of Alaska. Heavy fishing by foreign vessels during the 1970's led to a substantial population decline and fishery regulations in Alaska which sharply reduced catches. Data collection from sablefish fisheries in Alaska began in 1963. Catch, effort, age and length data have been collected to compute relative abundance indices 1 (catch/hook), age and length compositions. With passage of the Magnuson Fisheries Conservation and Management Act in 1976, foreign vessels fishing in U.S. waters were required to provide either fisheries research or markets for this privilege. This requirement sometimes is called the “fish-and-chips” policy. The Japan Fisheries Agency began a longline survey for sablefish in Alaska in 1978 as a “chip” to trade for continued commercial fishing for sablefish in U.S. waters. The Japan-U.S. cooperative longline survey was conducted annually from 1978 to 1994. In 1987, the AFSC began an annual survey intended to replace the cooperative longline survey so that a U.S. vessel, rather than a Japanese vessel, would conduct the survey for what had become a wholly U.S. fishery in 1988. The two surveys overlapped for several years to compare and test for differences between them and thus link the time series of standard longline surveys. By 1994, statistical analyses by Kimura and Zenger (1997) showed that enough data had been collected to complete a valid comparison. As a result, the cooperative longline survey was discontinued after 1994. The annual longline survey begun by the AFSC in 1987 has continued to the present. Survey objectives The survey objectives are: 1) Determine the relative abundance and size composition of the commercially important species: sablefish, shortspine thornyhead (Sebastolobus alascanus), Greenland turbot (Reinhardtius hippoglossoides) and rougheye and shortraker rockfishes (Sebastes aleutianus and S. borealis); 2) Determine migration patterns of sablefish, shortspine thornyhead, and Greenland turbot by tag and release methods; and 3) Determine the age composition of sablefish through otolith collections. Survey description The survey covers the upper continental slope and selected gullies of the eastern Bering Sea, Aleutians Islands region, and Gulf of Alaska (Figure 1). The survey covers nearly all areas where adult sablefish are found. Depths sampled during the survey of the upper continental slope range from about 150-1,000 m (82-547 fm). Sampling occurs during the summer and lasts 3 months. Survey operations are conducted using a chartered U.S. longline freezer vessel with overall length of about 55 m (150 ft). Survey gear The basic unit of survey gear is termed a skate. A skate consists of 100-m (55-fm) of line with 45 hooks spaced 2-m (6.5-ft) apart and baited with squid. A longline set consists of 80 skates with weights between each skate. The gear sinks to the sea floor where it samples fish near the bottom. Gear construction and configuration 2 Skates of gear are 100-m (55-fm) long and contain forty-five size 13/0 Mustad1 circle hooks (Figure 2). Hooks are attached to 38-cm (15-in) tied length (untied length 74-cm [29-in]) gangions secured to 46-cm (18-in) beckets tied into the groundline at 2-m (6.5-ft) intervals. Lengths of gangion and becket material are cut by burning. Gangion eyes are 10-cm (4-in) long. Hooks are hung by inserting the tied end of the gangion through the eye face closest to the hook tip (the inside of the hook). The groundline of each skate is marked with bright-colored flagging and red ink at the first and forty-fifth beckets, and with red ink at the remaining forty-three beckets. Five meters (16 ft) of groundline are left bare on each end. Skate eyes are 46-cm (18- in) long. The splice to form the eye is tapered, but the ends are not burned because the burned ends abrade the surrounding line when it is stretched. Gangion, becket, and groundline materials are medium lay #60 thread, medium lay # 72 thread, and soft medium lay 9.5 mm (3/8 in) American Line SSR 1001 (or equivalent nylon line), respectively. A set consists of 80 skates, is 8-km (4.3-nmi) long, and contains 3,600 hooks. Each end of a set has a flag and buoy array, followed by a buoyline made of 183-1,281 m (100-700 fm) American Line (length depends on water depth) and 92 m (50 fm) of 9.5-mm (3/8-in) polypropylene line, a 16-kg (35-lb) piece of chain to dampen wave effects on the buoyline, 92-m (50-fm) American Line, a 27-kg (60-lb) halibut anchor, 366-m (200-fm) American Line, and finally the groundline with hooks. Buoyline length varies with water depth and is 92-276 m (50- 150 fm) greater than water depth. The groundline is weighted with 3.2-kg (7-lb) lead balls attached at the end of each skate. The lead balls are tied to a stainless steel snap with a 20-cm (8- in) tied length polypropylene line of 6.2-mm (1/4-in) diameter. Measurement of hook spacing during gear construction A template is used to mark hook spacing during gear construction. NOAA personnel construct the longline skates in the Net Loft at the Alaska Fisheries Science Center in Seattle. The groundline is laid across the floor and stretched until straight. Painted marks on the floor spaced 2-m apart are used as a template to mark hook spacings with a red marker. Beckets are inserted at the red marks and gangions are attached. All construction except attachment of hooks is completed by NOAA personnel. Gear maintenance The gear is maintained to the following standard aboard the vessel. If the groundline is damaged in a short interval of line, the worn line is replaced by splicing such that the replacement line maintains hook spacing of 2 m. A splice consists of 3 tucks for each line end. Damage includes chafing, nicks, and wear. Gangions and beckets are replaced when the outer covering is worn or broken. Hooks are replaced when severely bent or broken. Slightly bent hooks are straightened. If the groundline is damaged over a long interval, the damaged skate is replaced with new gear built by NOAA personnel at the Net Loft. Citation of the above brand names does not constitute U.S. government endorsement. 3 Measurement of hook spacing during gear maintenance Marks placed 2-m apart at each baiting and repair station are used to measure hook spacing after splicing. Baiting of gear Bait specification East Coast or North Atlantic squid (Illex illecebrosus), 2-3 count per lb or larger, is the survey standard; Loligo or market squid is not acceptable. The general commercial designation is brown color, fit for human consumption (used as an index of freshness), 100-200 grams per squid. The mantle length should be 15-23 cm (6-9 in) long. Bait size The mantle is cut into 3-4 pieces, each 4-5 cm (1.5-2 in) long. Only the mantle and viscera are used for bait. The head and tentacles are not used for bait. Baiting method and quality Blocks of bait, usually 20 kg (44 lb) in weight, are taken from the freezer the evening before baiting.